Material separation



May 12, 1936. w. E; 'sAxE MATERIAL SEPARATION Filed.Jan. 11', 1954 ORE 550 [XHA usT REMOVABLE a /2 ENG/NE SCREEN CONCENTRA TE Inventor Walter E Sqxe.

Patented May 12, 1936- UNITED STATES PATENT OFFICE MATERIAL SEPARATION 14 Claims.

The present invention generally relates to methods of separating mixed substances, typically and more particularly to pneumatic concentration of ores, as when carried on in the devices commonly known as jigs. My improved method of dry concentration may be used on any suitable mixture and may be carried out in any suitable apparatus, a preferred apparatus for using this method in connection with ore being described in application Ser. No. 708,611, filed by me on January 27, 1934. I describe the invention as applied to ores as the process has been particularly developed for that purpose; but such description is not intended as a limitation on the process itself or its use.

Where possible, jigs have been generally of the hydraulic type. In many areas, however, it is not possible to obtain water for washing ores because of prior water rights annexed to all available water, entire absence of water, restrictions on disposals of tailings, and the like, or the high cost of obtaining water may make its use economically prohibitive in the case of ore having low recovery value.

For these reasons, jigs have been developed to use air as a concentrating fluid, and in general the theory of operation is the same as with water jigs, there only being a change in the concentrating fluid medium used. However, the use of air in place of and in the same manner as water has disadvantages because air requires a fairly well graded feed to the jig and does not make for close separation. The concentration of ore when carried on in a gaseous medium is termed dry in contradistinction to a wet process using a liquid medium for concentration, and the term Will be so used herein. It is not necessary that the mixture itself be without perceptible moisture though the present invention is particularly adapted to normally dry substances; but it is also adapted to separation of moist or damp mixtures and indeed, as will be mentioned later, it may be desirable to add water to the mixture.

The process of separating materials in an hydraulic jig is based upon the different rates of settling in a fluid medium of solid particles of different sizes and different densities. The settling in a jig is not free but is hindered since, by means of a piston or other movable member, the water is given a vertically reciprocatory motion through the screen over which the ore is passed so as to impart a like motion to the bed of material undergoing treatment, the upand down movements being termed pulsion and suction respectively. In theory, these strokes are equal in intensity and duration, but in practice, the pulsion stroke is made predominant by the continuous introduction of water into the 'jig, thus tending to damp out the suction and reenforce the pulsion stroke. The amount of suction may be regulated, Within limits, to best suit the materials handled.

One of the main differences between hydraulic and pneumatic concentration heretofore has been the absence in the latter of any true suction. The incompressibility of the water causes it to maintain a constant volume; thus movement of o expansibility of the air impedes, and at high rates of operation prevents, any downward movement corresponding to the water suction movement. Air concentration processes have not been able to use suction because of the practical difficulties of constructing apparatus in which the air is moved by means of an oscillating or reciprocating member so as to produce suction and yet operate at a sufficiently high rate to have a paying capacity. This is especially true since air concentration requires the jig to operate at a fairly high number of pulsions per minute because of the low viscosity of air.

The same lack of suction characterizes that mode of operation in which the air obtains its movement by the intermittent introduction into the jig hutch of compressed air, since pressure inside the hutch is never less than atmospheric. Particularly in this process, but also in the air process mentioned above, the compression of the air acts on the particles of gravel for an appreciable lengthpf time at each pulsion because of the slow release of energy stored by the elasticity of the air; and as the number of impulses per minute increases, the distinctness between each impulse decreases resulting in a tendency for the impulses to merge and produce a continuous-upward force of fluctuating value.

Briefly, both wet and dry, and particularly these dry concentration processes have been characterized by the lack of sudden impact imparted to the ore, and by the lack of a sharp low pressure, or relative suction, following each impact.

It is thus a general object of my invention to produce a method of pneumatic concentration of ore which produces sharply distinct impulses of extremely short duration acting upon the particles of ore.

It is also an object of my invention to evolve a pneumatic concentration process that produces suctionso that the fine concentrates are more quickly and certainly brought down, and so that the individual impulses are more distinctively separated.

The annexed drawing is a diagram showing the relation of the parts referred to in the following description.

The above objects are attained by passing the material to be treated, for example placer gravel, over a generally horizontal, stationary screen, with feed at one edge and the tailing discharge at the other. An enclosure, called the hutch, forms a chamber open to the under side of the screen, and into which chamber I intermittently introduce heated gas under pressure, each admission being so short and sudden and at such pressure as to lift particles by impact rather than by an upward'fluid movement faster than the settling rate of the particles,.and enduring for such time as to carry the particles upwardly. By reducing to a minimum the time of each impulse, the force applied may be enormously increased, and at the same time so controlled that the impact energy communicated to the particles is suflicient to raise the low density particles but not to raise the high density particles.

Although my invention contemplates any suitable means of producing the desired air movements, I prefer to produce them by means of a series of controlled explosions either within the hutch or within a diiierent chamber adapted to be placed in communication with the hutch. As an example of the former method, acetylene or other explosive gas may be introduced into the hutch and exploded by an electric spark, the rate of gas ilow and frequency of sparking controlling the operation. An example of the latter method is the introduction into the hutch of the exhaust from one or more cylinders of an internal combustion engine. A device using this latter method is disclosed in my companion case referred to above and illustrated diagrammatically here. g V

In this diagram, the hutch I0 is shown to be supplied with heated gases via the exhaust pipe I! from one cylinder of engine 12. The screen is is fed with material from chute M at one side, the reject from the screen passing over tail board l5. Hutch I0 is also shown connected to a fan Hi.

It makes no difference in the process whether the explosion takes place in the hutch or in another chamber from which the exhaust is admitted to, the hutch by a valve for under either circumstance the hutch is immediately filled with a very hot gas under pressure formed as a product of combustion. The only difference made by the interposition of a valve (the cylinder exhaust valve is perhaps to lessen the force of the explosion, which loss can easily be compensated for by increasing the explosive charge. 7 a

The desired force of impact will vary with the materials handled, but in general will be sufficient to lift the low density particles, except the very large ones, but insufficient to lift the high density metalliferous particles which settle downwardly onto the screen through the ore that is kept in a loose, mobile state by the successive impacts. Regulation of the force to the proper value to move the low density fines to the top of the ore bed so that they will pass off at the discharge may be accomplished by control of the engine explosion in several ways.

These methods of control include adjustment of the exhaust valve setting to determine the length of its open period, advancing or retarding the spark or time of firing relative to the valve opening, and increasing or decreasing the load on the engine, the speed of the engine, or the quantity of explosive mixture admitted to the cylinder.

It will be seen that there are available several Ways of controlling the character of the heated gas and its introduction into the hutch in order to regulate the magnitude and frequency of the impacts to secure the best operating conditions; and it is also possible to change the magnitude of the impacts independently of the frequency or both together by proper balancing of the load on the engine and the quantity of charge admitted to the cylinder.

As is well known, explosive mixtures depend primarily upon the heat liberated during the ex othermic reaction to greatly heat the gaseous products of combustion in order to develop high pressure, rather than upon a mere increase in volume in product as compared with the reagents. By way of example, two volumes of acetylene react with live volumes of oxygen to form only six volumes of product. Thus the pressure rise by volume increase alone is negligible, but the almost instantaneous temperature of several hundred degrees centigrade heats the products of combustion to rapidly expand the gas, thus building up a high pressure for a short time; High pressure within the hutch collapses almost as rapidly as it is built up, partly because a portion of the gas is forced through the bed of gravel, but chiefly because the heat in the, gas is rapidly dissipated,

causing it to contract to a volume and density comparable to that before combustion. This contraction is substantially complete before the After the initial pressure has forced part and pressure is less than the hutch volume, a sub-.

atmospheric pressure is produced that imposes a suction on the gravel. The volume of gas admitted can of course be controlled in the manner specified above. This suction aids in rapid working of the gravel; but it is not essential to satisfactory operation of my improved process that sub-atmospheric pressure be formed within the hutch since, as will be seen, the impacts are sufllciently distinct to eifectively concentrate ore without positive downward air movement or force. It is only necessary that there be a relatively low pressure period, or relative suction, sharply succeeding each high pressure impact.

Because of the extreme rapidity with which the pressure is built up and falls, impact blows may be applied to the gravel at suitably high rate, say 1000 to 1200 per minute or more, without causing the impulses to merge and destroy the suction effects between impulses.

Because the time during which the gas pressure is exerted is so short as to be almost infinitesimal, an impact force great enough (if it were of sufficient duration) to blow all the gravel completely off the screen may be applied and still keep the material closely on the screen. However, the gangue or gravel will contain large particles of sufficient m'ass not to be lifted upward by the impacts, and these large particles, along with the heavy fines, will form a bed on top of the screen of a depth equal to the tail board height at the discharge. Initially the bed is composed mainly of gangue, but as the process is carried on the proportion of fine concentrate increases. Side pressure from the feed forces all gangue over the bed to the discharge, while the heavy fines have been permitted to settle out; and these fine concentrates containing the desired metal will filter down through the interstices of the bed of gangue and eventually rest on the screen displacing the coarse gangue upwardly, unless the heavy fines are small enough to fall through the screen into the hutch.

In such instances as those where the particles of ore are held together by some water soluble clay, water may be poured over the ore bed, the excess draining into the hutch. The water loosens the particles of different substances that may be cemented together, and so makes for a better separation. The water also acts in some measure as a lubricant. Although I prefer to proceed without water, since later drying is thus eliminated, yet the use of water as mentioned in no way changes the process, for the heated gas, not the water, is the fluid medium transmitting the impacts and effecting the concentration.

When concentrating ores that must be maintained dry, the invention contemplates the use of a continual draft of air moving through the hutch under a small head, say 3 to 6 inches of water, in order to ventilate the hutch and remove the products of combustion so the water vapor formed by the explosion will not condense and dampen the fine concentrates.

The continuous stream of air may pass either upwardly or downwardly through the ore bed. If the head of the upwardly moving stream is increased it may be used, in some measure, to help support the ore bed and keep it loose and mobile as well as ventilated; and if the stream is directed downwardly through the bed it may be used to help keep down dust. In either case the impacts from the explosions are superimposed on the constant air stream, and act exactly as described except that the pressure curve is shifted bodily from its position when no air stream is used, accordingly as the impacts are reinforced or opposed by the air stream. The direction of the air flow is controlled by rotating the fan to act as a blower or suction fan, as desired.

If the fan sucks air and exhaust from the hutch at approximately the same rate as exhaust is introduced, then the separation above the screen will take place in substantially a static atmosphere. Increasing the suction head of the fan draws air downwardly through the ore bed; and experiment has shown the concentration takes place as before, but there is a slight decrease in the rate at which material moves across the screen from feed to discharge, and an increase in the amount of fine material passing into the hutch.

This last operating condition is favorable to the sizing or screening of a homogeneous material such as ground cement or pigment which is very fine and already closely sized. The impacts are adjusted in strength to keep the material above the screen loose and mobile without blowing it off the screen. The down draft then carriesthe finer particles through the screen into the hutch. Screening is very rapid and separation can be accomplished according to variation in size rather than in density.

In all concentration, the materials rest but lightly on the screen so that wear of the screen is very small in comparison with ordinary screening methods.

In summary, it will be seen that I preferably use the products of combustion resulting from an explosion to provide a charge of gas at high temperature. Because of its temperature, it expands and exerts a sudden, sharp force on all particles above the screen. The rapid cooling of I this gas contracts it to a much smaller volume near or below atmospheric pressure with two results: The duration of the impulse exerted is so short as to be almost infinitesimal, and a distinct low pressure or relative suction is produced between impulses. The short time of the impulse allows the use of a relatively large force, so large that were it to continue for the time of pulsion in the usual jig processes, which is long enough to allow the particles to acquire approximately the maximum velocity of the moving fluid medium, all the gravel would be blown away. Thus I separate by applying rapidly succeeding and sharply defined impacts to the material rather than by allowing the particles to settle in a moving fluid medium. The force of the impact blow is controlled by regulating the explosive charge, and may be controlled closely to effect a. clean separation of metallic particles without requiring any particular preliminary sizing of the feed to the screen. The range of size and density of particles in the feed, and whether coarse or fine concentrates are to be saved, will determine the magnitude and frequency of the impacts satisfactory for separation under the given conditions, and those skilled in the art will understand how to regulate and adapt the process to any suitable ore.

The results attained by my system, due to its sharply defined impact action, are far superior to any before obtained in an air jig, and, as far as I am aware, superior to those obtained in water jigs. This is true both as to operation efiiciency (ratio of operation cost to materials concentrated) and as to concentrating eificiency. Tests so far conducted have shown a concentration and recovery efficiency of nearly 100% for finely divided metals in gravel, sand and clay gangues.

It is to be understood that the foregoing i intended to be illustrative of rather than restrictive upon broader claims appended hereto, for various changes in procedure may be made without departing from the spirit and scope of the invention. The application of the process to separation of foreign materials, such as pieces of metal or stone, from dry granular substances like grains, sugar, and so on, will be readily apparent, as well as the use of the process to separate homogeneous materials according to size. Likewise, it will be apparent that the charges of heated gas may be formed in some other manner than by an explosion, as for example by live steam from a boiler; and the gas used may be other than the exhaust products from an engine.

I claim:

'1. The process of concentration of mixed substances that includes subjecting the mixture to impacts from successive charges of heated gas under pressure, and to alternating relative suctions produced by rapid cooling of the gaseous charges.

2. The process of concentration of mixed substances that includes subjecting the mixture to successive impacts from successive charges of heated gas, under pressure produced by successive explosions.

3. The process of concentration of mixed substances that includes subjecting the mixture to successive impacts produced by the hot expanding products of combustion derived from successive explosions.

4. The process of concentration of mixed subsuccessive impacts produced by introducing beneath the bed the hot expanding products of combustion derived from successive explosions.

7. The process of concentration of mixed substances that includes, forming a moving bed of the mixture, and subjecting the mixture bed to alternate impact and suction by introducing beneath the bed a charge of highly heated gas under high pressure and rapidly cooling the gas to substantially atmospheric temperature.

8. The process of concentration of mixed substances that includes, forming a moving bed of the mixture, and subjecting the mixture bed to alternate impact and suction by introducing beneath the bed a charge of highly heated gas under high pressure and rapidly cooling the gas, thereby rapidly lowering its pressure.

9. The process of concentration of mixed substances that includes, forming a moving bed of the mixture, and subjecting the mixture bed to impacts from successive charges of heated gas produced by successive explosions beneath the bed of a combustible mixed with air.

10. The process of concentration of mixed substances that includes, forming a moving bed of mixture, and subjecting the mixture bed to al ternate impact and suction by introducing beneath the bed the hot exhaust from a cylinder of an internal combustion engine and rapidly cooling the exhaust to substantially atmospheric temperature.

11. The process of concentration of mixed substances that includes, forming a moving bed oi. the mixture, subjecting the mixture bed to impacts from successive charges of heated gas produced by successive explosions beneath the bed, and maintaining a continuous draft through the bed to carry away the cooled products of combustion.

12. The process of concentration of mixed substances that includes, forming a moving bed of the mixture, and subjecting the mixture bed to successive impacts produced by introducing beneath the bed the succeeding charges of hot expanding products of combustion derived from successive explosions of a combustible mixed with air.

13. The process of concentration of mixed substances that includes, forming a moving bed of mixture, subjecting the mixture bed to impacts from successive charges of heated gas produced by successive explosions beneath the bed, and maintaining a continuous draft downwardly through the mixture bed.

14. The process of concentration of mixed substances that includes subjecting the mixture to a substantially constant stream of gas and to high frequency impacts superimposed upon the constant stream and produced by successive charges of heated gas under pressure introduced into the constant stream.

WALTER E. SAXE. 

